1. Field of the Invention
The invention relates to a method of producing microstructural medical implants by laser material processing and in particular by the laser cutting of bioresorbable vessel wall supports.
2. Background Art
As for the background of the invention, numerous implants are known in medical technology, which consist of medical technological materials such as metal alloys or polymers and are structured by cutting processes. Vessel wall supports for use in the human heart are to be mentioned by way of example; they are denoted as "stents" in technical language. So as to avoid unnecessary irritation of the implant contacting tissue, for instance the inside wall of a blood vessel of the heart in the case of an intravascular stent, the edges of the implant structure are to be as smooth and flash-free as possible.
The prior art teaches to manufacture microstructural medical implants by laser cutting processes that originate from conventional material processing technology. Fundamentally, the use of lasers permits the production of microstructures at a high precision and a high working speed.
As a rule, the conventional laser cutting processes mentioned make use of continuous-wave lasers or possibly tunable lasers of pulse lengths in an order of magnitude ranging from nanoseconds to milliseconds. Consequently, the time of action of the laser on the material at the respective spot of machining is so long that in addition to the job of material cutting, considerable heat build-up is produced in the microenvironment of the edge of cut. Minimal quantities of the material are melted, which rigidify irregularly after the time of action of the laser beam or in between the individual pulses of long duration. This causes disadvantageous flashing of the edges of cut.
The flashing mentioned above requires aftertreatment jobs for deflashing. A customary method therefor is electropolishing, which is however very complicated regularly and produces only minor improvements. Further, electropolishing cannot be used because of the low electrical conductivity of many materials, in particular polymers.
So as to avoid the mentioned drawbacks, use may be made of an alternative cutting method such as electrical discharge machining. This is accompanied with an increase in the time consumed for material working as well as a reduction of precision. Owing to the low electrical conductivity of polymers, the use of electrical discharge machining is not possible with these materials.
Finally attention is drawn to the fact that a process for laser material processing is known from WO 95/27586 A, using very short laser pulses in the range of femtoseconds. Various samples such as a gold assay, a sheet of glass and a sample of body tissue (cornea) are exposed to short laser pulses in the range of femtoseconds, microscopical holes and ablation spots being created thereby.